First thing to do: get your friend out of the loop. If anything he's more motorcar challenged than you, and that's something.
Losing coolant is a major event and requires "grounding" the car until it is discovered and repaired. The consequences of not doing so are more often than not an engine replacement or rebuild whose cost can exceed the residual value of the car.
For future reference, The first thing to check is obvious wet spots on the car or under it. The next is white vapor emanating from the exhaust after the engine has got to normal operating temperature.
Invisible leaks plus overheating lead to suspecting water pump bearing or gasket failure. The water accumulates at the bottom of the timing belt cover, and when deep enough, the timing belt carries it up into the rocker cover where it dissipates all over the place: sometimes a "damp when hot" smell in the engine compartment is the only clue.
Once it has done in the head gasket or cracked the liner, it can trickle into one or more cylinders and apart from its corrosive effects, it can obstruct free piston motion at the top of the stroke resulting in absolutely horrendous engine damage.
From the sounds of things, you paid the price of an engine to join this forum. For future reference, get an owners manual (even if its not for your car specifically), and carefully read up on the things that make immediate professional intervention a "must do". Loss of oil pressure, coolant, and brakes are invariably at the top of the list.